NON-INDIGENOUS BRITISH BIRDS. 303 



lagoons, on low sandy islands, and on the flat, sandy 

 shores of inland salt-lakes. Doubtless this Tern pairs 

 for life, returning as it does with great regularity to 

 certain breeding places. The nest is of the scantiest 

 description, a mere hollow in the sand, sometimes, but 

 not always, with a few bits of sea-weed or dry grass 

 round the rim. When disturbed at their breeding place 

 the birds rise and hover in the air above their nests, 

 becoming very clamorous, and boldly swooping down 

 round the head of the intruder. 



Range of egg colouration and measurement : 

 The eggs of the Caspian Tern are two or three in 

 number. They vary in ground colour from creamy- 

 white to buffish-brown, spotted with dark brown, and 

 with underlying markings of gray. The surface mark- 

 ings are not very large, and generally pretty evenly 

 distributed, but sometimes most numerous on the major 

 half of the Ggg, and forming an irregular zone. Occa- 

 sionally a few streaky spots occur amongst the others, 

 and the underlying markings are often large and gener- 

 ally conspicuous. Average measurement, 2'55 inches 

 in length, by 17 inch in breadth. Incubation, according 

 to Meyer, lasts about twenty days, but whether both 

 parents assist in the duty is not known. 



Diagnostic characters : The eggs of the Caspian 

 Tern are distinguished from those of all other Terns by 

 their large size, with the possible exception of those of 

 vS. maxima. 



